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Big mistake mounting horizontal stab...

Michael Burbidge

Well Known Member
Friends,

If one hole can ruin an airplane, I might have done it. I am so discouraged!

A few nights ago I mounted my horizontal stabilizer. I thought everything went pretty smoothly and was pleased with my work. Well today I got looking at the holes that were drilled through the HS-908 attach angles into the F-714 deck and I discovered a big problem that I didn't know existed.

I noticed a slight notch on one side of one of the holes. When I got looking at it closer it was the entry point of the initial #40 hole I had drilled through the attach angle and into the deck below. But when I looked closer I saw that the #40 hole went off at a pretty sharp angle. I remember that I made that initial hole with a 6 inch bit and that I saw that the tip bent and went in at an angle. But I had no idea it bent that much. When I enlarged the hole to a #12, I made sure to straighten out the angle, and thought everything was fixed at that point. But as can be seen from the photos below the angle was more dramatic than I was aware of at the time. There's a photo from the top and from below.

I have no idea how I would go about fixing this. With some trouble I can remove the deck and replace the bottom angle, but I have no idea what I would need to do about the longeron, which obviously has a somewhat enlarged hole in it.

Thanks for any suggestions you might have,
Michael-

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Your pictures are really good - I would send them to Vans on Monday and ask their opinion, but I'm betting they will tell you to drill it out to the next AN bolt size and build on. Worse mistakes than this have been made and corrected. The edge distance on the off-angle hole is into the direction of the web of the angle where you have excess material, this is the best of a bad situation.

I'm not a mechanical engineer, and I'm not telling not to panic - I'm just telling you not to panic until Vans says panic. At this stage in the build there are about seventeen hundred other items you can work on for a week until you get an answer.
 
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Don't get too discouraged Michael! We've all had those moments when we've wondered if we've really messed something up. Let us know what Van's says.
 
Also keep in mind ...

... The primary force on the HS is downward. It's not like there will be constant or significant loads pulling upward on that rr deck. I suspect drilling out to the next larger bolt size will work, but Vans can/will confirm or deny that.
 
I did the same thing. Twice.

Don't feel bad about it, I did the same thing only I did it twice. I noticed the mistake before riveting though and opted to replace all the affected parts. It was the most expensive mistake on the whole plane at about $200 +/-. I was later able to use the scrap parts elsewhere in the plane as stiffeners, etc.

I've learned two things building the plane:
1. I'm going to mess things up occasionally.
2. Anything I mess up, I can usually fix.
 
fill-n-drill?

Would it be considered acceptable to fill the holes with JB-Weld and re-drill?
 
I was thinking along the same lines, though I'd still check with Van's. Since it's so very near the end of the longeron, you could fill the holes, back up the longeron with a 1/16" thick piece of aluminum stock, and redrill. Then use a slightly longer bolt through the redrlled hole and backing piece. I'd probably make the backing piece long enough that both bolt holes pierced it.
 
On the wall of my hangar ....

"Any mistake can be fixed. Sometimes with time, sometimes with money - - but usually both." :D
 
As suggested, call Van's. If it was my plane I would replace the underlying angle at the very least. I have some concerns that the additional hole in the main longeron weakens that primary structure. JB weld is a great product, and has it's uses, but all it is going to do here is make you feel better. It is not going to remove the stress point.
Van will likely tell you to replace the underlying angle and move on but do get their opinion and follow their advice.
 
I've been around aircraft stuctures a long time and have seen quite a few repairs in the certified world and my opinion here is you really don't have much to worry about. There would have to be a tremendous negative-g force required to fail this joint as-is. For this joint to fail the longeron would have to bend out of the way, and angle attached to the bulkhead would have to be ripped from it. Going the other way (compression), all the bolt is doing is holding the HS in position with virtually no load. You could put a triangular reinforcement, a shim forward of the angle underneath the longeron, and bolt this in to add some more strength to this joint.
 
As suggested, call Van's. If it was my plane I would replace the underlying angle at the very least. I have some concerns that the additional hole in the main longeron weakens that primary structure. JB weld is a great product, and has it's uses, but all it is going to do here is make you feel better. It is not going to remove the stress point.
Van will likely tell you to replace the underlying angle and move on but do get their opinion and follow their advice.

I agree with Tom, see what Van's says, they are the only ones that know the stress in this area and can recommend a repair if possible.

Not sure how this happened, but for critical holes you should always drill a small pilot hole to verify location before stepping up to full size. If necessary you can "pull" a pilot hole to correct the location before stepping it up.
 
Mis-drill

As someone with 30 years as a A&P and who has worked on the Eclipse and X-47-B prototypes, if it was my airplane I would change the part. Realistically it would probably be OK as is, but call Vans.
JB Weld HAS NO PLACE ON A AIRCRAFT!
If you really want to drill straight holes in future get a set of drill bushings.
 
Freeze plug

Or you can install a freeze plug. (Not the car kind).
 
First off, as has been repeated above, call Vans.

My concern is the piece of angle under the one you are showing in the photo. Gray in color, and rivets in it.

If I am interpreting this correctly, you are seeing the longeron to the right and lower in the photo, but the cross piece is covering the damaged area of the longeron.

I would suggest removing the short cross piece of angle, and getting a photo of the longeron and posting it also---and sending that to Vans for their inspection/recommendation.

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Michael,

I agreer with Rocketbob.

I discovered a simular (but worse, hole in the project I bought) the hole in my project actually notched the edge of the longeron. It was invisible except by mirror and flashlight.

My solution After a month of stewing was as follows.
Under the HS-908 attach angle is the F-798 shim. It is a 1/8" spacer shim.
I enlarged the shim to include two rivets in front and two rivets behind the offending hole ( sort of a splint on the longeron) drill out and replace the four longeron rivets and also replace the F-710B angle and the HS-908 then build on.

Vans approved this several years ago.

The normal flight forces are down at that location. My thinking is that, if you are pulling out that mounting bolt at that location you currently have other important issues to deal with.

My $0.02.
 
Straight holes

Appears that the two large holes are at different angles. One of the hardest things to do in sheet metal work is drilling a round, straight hole.
On the XB-47-X project we were required to use drill bushings as we were going through .250 - .500 titanium and using hi-loks.
 
Horizontal stab bolts

I suspect that if you drill it out to an AN4 bolt you will have a edge margin problem and even worse the nut will likely hit the longeron angle and not fit onto the bolt correctly. I would replace the angle but let the good folks at Vans be the final authority.

Pete
 
The same thing happen to me and I remember being pretty sick about it. I actually happen to be traveling by Van's at the time and stopped in to see them. Below is a picture of what they approved, you have to have a shim anyways, this is just a enlarged version of it tying everything together. I remember the engineer saying that it was over kill, but better than replacing parts.
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Approved fix...

The fix that Vans tech support suggested was similar to the fix that Steve took.

They said the following.

Make a triangular gusset and use that on the top of the deck to replace the spacer that sits underneath the HS-908 attach angle. Make the gusset big enough to take in one rivet in front of the attach angle and one rivet inboard of the attach angle. They also suggested filling the extra hole with JB Weld, not to increase the strength of the longeron or angle underneath, but to provide compression against the bolt. They said the forces in this area are downward.

They said for a cleaner fix I could also replace the angle underneath, but that it was not necessary.

I'm currently stewing over whether I am going to replace the angle underneath. I cannot possibly see how I can drill out the rivets that attach the angle to the bulkhead without removing the deck. I put the manufactured head on the aft side of the angle and bulkhead on the two outer most rivets. Accessibility to the manufactured head of those rivets is nearly impossible. All the rivets on the deck are very accessible and should be easy to drill out. But there's always a chance of messing up a few of those rivets.

This fix is specific to my mistake. I would not suggest anyone use this same fix without consulting with Vans.

Thanks for all the input,
Michael-
 
Fixed...

I finally finished the fix today. I've been traveling a bit and so this task got strung out a bit.

I'm very pleased with the results. I did decide to replace the angle. I removed the top deck which went very smoothly. No enlarged holes from drilling out rivets. Then I removed the old angle. I filled both holes (the small angled pilot hole and the bolt hole) in the longeron with JB weld. Later I re-drilled the bolt hole so that JB weld only remained in the angled pilot hole.

I fabricated a new angle and installed it. Before re-installing the top deck, I fabricated the gusset. Actually I made one for each side just so they match. It looks nicer. I then match drilled the gussets to the top deck so I didn't have to back drill through the holes to install the gussets.

I then re-installed the top deck, and finally installed the gussets.

Here's a couple of photos.

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Very nice job with this. Wouldn't your HS seat on that one single rivet next to the bolt holes? If memory serves me right, there may be a bit of interference and you may need to replace those two rivets with flush head rivets.
 
No interference...

I just bolted the HS to the tail. I don't have an interference problem with the rivets you mention. I can easily slip a piece of card stock in there.

Thanks,
Michael-
 
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